Finely divided solids or particles, commonly referred to as fillers, are often added to polymer systems to produce a variety of solid, essentially nonporous, composite materials. Fillers are typically added to polymeric materials for the purposes of either improving physical properties or reducing overall cost. These fillers are primarily inert, unreactive particles, chosen largely according to their compatibility with the matrix polymer and/or their inexpensive nature. Typical of such fillers are minerals, clays, metallic powders, inorganic oxides, glass, talc, wood powder, and carbon black.
Porous, particle-filled composite articles are also known in the art. These materials find use in such applications as filtration or separation media, or in other applications where permeability to gases or liquids is required.
U.S. Pat. No. 4,957,943 describes a microporous particulate-filled thermoplastic polymeric article which may be in the form of a film, a fiber, a hollow fiber, or a tube. The particulate filler is of submicrometer or low micrometer size and may be a metal, a metal oxide, or a carbonaceous material such as carbon black. These composites are useful as protective garments or as X-ray or electromagnetic shielding materials.
U.S. Pat. Nos. 4,550,123 and 4,342,811 describe microporous polymeric fibers and films which contain particles capable of sorbing vapors, liquids, and solutes. Typical sorbent particles include active carbon, silica gel, and molecular filter type materials.
In addition to particulate-filled microporous materials described above, it is also known to incorporate particles into macroporous fibrous webs or sheet materials. For example, U.S. Pat. No. 3,971,373 describes a porous sheet product comprising a web of entangled melt-blown organic polymeric microfibers and a three dimensional array of solid particles uniformly dispersed and physically held in the web. Typical particles are activated carbon or alumina. The composite sheets are useful for adsorbing organic or acidic vapors from an air stream. U.S. Pat. No. 4,963,431 discloses a permeable, nonwoven polymer pad having zeolite particles adhesively bonded throughout the pad. This pad is useful for absorbing ammonia from a fluid.
U.S. Pat. No. 4,153,661 describes a uniformly porous, high void-volume composite sheet comprised of a particle material uniformly distributed throughout a matrix formed of interentangled, fibrillated polytetrafluoroethylene (PTFE) fibrils. The described particles are primarily inorganic particles. U.S. Pat. Nos. 4,373,519 and 4,460,642 describe the incorporation of hydrophilic, organic, water-swellable particles into a fibrillated PTFE matrix. Preferred composites contain particles of crosslinked dextran and are useful as a wound dressing. U.S. Pat. No. 4,810,381 discloses a composite chromatographic article comprising a PTFE fibril matrix and a non-swellable sorptive particle enmeshed in the matrix. Preferred particles are inorganic oxides such as silica and zirconia.
The immobilization of proteins or enzymes on insoluble, solid supports has long been recognized as being desirable. Immobilization allows easy recovery and reuse, and often enhances stability, of biologically active molecules. Methods of immobilization range from physical adsorption, to physical entrapment, to ionic or covalent bonding of the biologically active molecule to the support.
U.S. Pat. No. 4,855,234 discloses a composite article provided by subjecting a fibrous support in sequence to a surface modification treatment, a coating of a protein immobilizer compound, and a biologically active protein. U.S. Pat. No. 4,963,494 describes an ultrafiltration membrane having an enzyme immobilized thereon. Immobilization is accomplished by impregnating a membrane with a solution of a water-soluble polymer, utilizing a crosslinking agent to crosslink the polymer within the pores of the membrane, then covalently binding the enzyme to the membrane through functional groups of the crosslinked polymer.
U.S. Pat. No. 4,102,746 discloses proteins such as enzymes immobilized on a microporous binder or matrix having finely divided filler particles dispersed throughout the binder. Proteins are covalently coupled via a chemical bond to dispersed filler particles in the microporous material, using bridging agents in a two-step procedure.
U.S. Pat. No. 5,041,225 discloses a hydrophilic, semi-permeable membrane of PTFE having internal and external surfaces coated with a complex of a hydrophilic polymer which adheres to the membrane structure and a complexing agent. The complex renders the PTFE membrane hydrophilic and protein affinitive. Preferred complexing agents are boric acid, sodium borate, or sodium chloride.